Sterilization is the absolute destruction of any virus, bacteria, fungus or other micro-organism, whether in a vegetative or in a dormant spore state. Conventional sterile processing procedures for medical instruments involve high temperature (such as steam and dry heat) or toxic chemicals (such as ethylene oxide gas, EtO). Steam pressure sterilization has been the time-honoured method of sterilization. It is fast and cost effective. However, the autoclave destroys heat-sensitive instruments. Thus, since more and more heat-sensitive instruments such as arthroscopes and endoscopes are used in medical treatment, other types of sterilization need to be used.
Ethylene oxide sterilization is used to cold sterilize heat-sensitive instruments. Until recently, ethylene oxide sterilization was the state of the art method for cold sterilization. Ethylene oxide sterilizes heat and moisture-sensitive objects and penetrates very well. However, it has been deemed by national health and safety organizations to be carcinogenic and neurotoxic.
A more efficient, safer, and less expensive sterilization agent has been found in the form of ozone O3. Ozone can easily be generated from oxygen, which is readily available in the hospital environment, usually from a wall or ceiling oxygen source, or, if mobility is required, from a portable “J” cylinder of oxygen.
Ozone generally acts on chemical compounds. Either by direct reaction or through hydroxyl radical species formed during the decomposition of ozone (Encyclopaedia Of Chemical Technology, Vol. 17, Ozone page 953 to 964). The sterilizating activity of ozone increases rapidly with increased relative humidity. The resistance of spores to ozone varies from strain to strain, but the differences become comparatively small at high relative humidity (Ishizaki et al., 1986. Inactivation of the Silas spores by gaseous ozone, J. Appl. Bacterial, 60:67-72). The presence of water often accelerates ozone reactions with organic substances (Langlais et al., (EDS), 1991, Ozone in Water Treatment, Application and Engineering. Louis Publishers: Chelsea, Mich., 569 pages).
The use of a mixture of ozone gas with a very fine water mist in a sealed plastic bag container which contains an article to be sterilized is described in U.S. Pat. No. 3,719,017. U.S. Pat. No. 5,069,880 describes a device capable of generating a high relative humidity by bubbling ozone gas through a water bath in an effort to increase the water content of the gas. However, using such a high humidity may lead to condensation of water on the articles to be sterilized. Condensation is not only undesirable, but must be avoided, since it prevents direct access of the ozone gas to organisms on the surface to be sterilized. PCT CA2002/01720, which is incorporated herein by reference in its entirety, describes an ozone sterilization method including a temperature equalization step for bringing the article to be sterilized to substantially the same temperature as the sterilization atmosphere, so that condensation is avoided as much as possible. This is achieved by multiple cycles of evacuating the sterilization chamber and re-introducing ambient air. Such a method is time consuming due to the repeated evacuation and re-filling of the sterilization chamber. Thus, an improved method is desired.